Transcript competition

Population Ecology
I. Attributes
II.Distribution
III. Population Growth – changes in size through time
IV. Species Interactions
V. Dynamics of Consumer-Resource Interactions
VI. Competition
VI. Competition
A. Overview:
1. Types:
- exploitative/scramble – organisms remove
what they can; neither gets enough to
maximize fitness
VI. Competition
A. Overview:
1. Types:
- exploitative/scramble – organisms remove
what they can; neither gets enough to
maximize fitness
- territorial/contest/interference – competition
for access to the resource, with ‘winner take
all’. Winner still incurs cost of competition
VI. Competition
A. Overview:
1. Types:
2. Outcomes:
- Reduction in organism growth and/or pop. size (G, M, R)
- Competitive exclusion (N = 0)
- Change range of resources used = resource partitioning.
VI. Competition
A. Overview:
1. Types:
2. Outcomes:
- Reduction in organism growth and/or pop. size (G, M, R)
- Competitive exclusion (N = 0)
- Change range of resources used = resource partitioning.
- If this selective pressure continues, it may result in a
morphological change in the competition. This adaptive
response to competition is called Character Displacement
Character Displacement
VI. Competition
B. Empirical Tests of Competition
1. Gause
P. aurelia vs. P. caudatum
Both do well when alone,
but P. aurelia outcompetes
P. caudatum when
together
VI. Competition
B. Empirical Tests of Competition
1. Gause
):
P. aurelia
vs. P. bursaria
VI. Competition
B. Empirical Tests of Competition
1. Gause
):
P. aurelia
vs. P. bursaria – coexist when together
VI. Competition
B. Empirical Tests of Competition
1. Gause
P. aurelia and P. caudatum feed on bacteria in the open water (same
niche); P. bursaria feeds on bacteria on the glass.
“Competitive exclusion principle” – Two species with the same
environmental requirements (niche) cannot coexist.
VI. Competition
B. Empirical Tests of Competition
Competition between two species
of flour beetle: Tribolium
castaneum and T. confusum.
1. Gause
2. Park
Tribolium castaneum
TEMP
HUM
T. casteum
won (%)
T. confusum
won (%)
COOL
dry
0.0
100.0
COOL
moist
29.0
71.0
WARM
dry
13.0
87.0
WARM
moist
86.0
14.0
HOT
dry
10.0
90.0
HOT
moist
100.0
0.0
VI. Competition
B. Empirical Tests of Competition
Competition between two species
of flour beetle: Tribolium
castaneum and T. confusum.
1. Gause
2. Park
HUM
T. casteum
won (%)
T. confusum
won (%)
dry
0.0
100.0
moist
29.0
71.0
WARM
dry
13.0
87.0
WARM
moist
86.0
14.0
HOT
dry
10.0
90.0
HOT
moist
100.0
0.0
TEMP
Competitive outcomes
COOL
are dependent on
complex environmental COOL
conditions
Basically, T. confusum wins when it's dry, regardless of temp.
VI. Competition
B. Empirical Tests of Competition
Competition between two species
of flour beetle: Tribolium
castaneum and T. confusum.
1. Gause
2. Park
HUM
T. casteum
won (%)
T. confusum
won (%)
dry
0.0
100.0
moist
29.0
71.0
WARM
dry
13.0
87.0
WARM
moist
86.0
14.0
HOT
dry
10.0
90.0
HOT
moist
100.0
0.0
TEMP
Competitive outcomes
COOL
are dependent on
complex environmental COOL
conditions
But when it's moist, outcome depends on temperature
VI. Competition
B. Empirical Tests of Competition
1. Gause
2. Park
3. Connell
Intertidal organisms show a zonation
pattern... those that can tolerate more
desiccation occur higher in the
intertidal.
3. Connell - reciprocal transplant experiments
Fundamental Niches defined by physiological tolerances
increasing desiccation stress
):
3. Connell - reciprocal transplant experiments
Realized Niches defined by competition
):
Balanus competitively
excludes Chthamalus
from the "best" habitat,
and limits it to more
stressful habitat
VI. Competition
B. Empirical Tests of Competition
1. Gause
2. Park
3. Connell
4. Emery et al. (2001)
4. Emery et al. (2001)
Add nutrients and the more
salt tolerant species, which
was competitively excluded
from more benign habitats
under lower nutrient
conditions, now expands –
nutrient limitation is
relieved and the tolerant
species wins.
VI. Competition
C. Modeling Competition
1. Intraspecific competition
The logistic curve describes
intraspecific competition.
VI. Competition
C. Modeling Competition
1. Intraspecific competition
2. Interspecific competition – Lotka-Volterra Models
The effect of 10 individuals
of species 2 on species 1, in
terms of 1, requires a
"conversion term" called a
competition coefficient (α).
So, here, 10 N2 individuals exert as
much competitive stress on N1 as 20
N1 individuals…so α = 2.0 and N1
equilibrates at K – 20.
VI. Competition
C. Modeling Competition
1. Intraspecific competition
2. Interspecific competition – Lotka-Volterra Models
We can create an "isocline" that
described the effect of species 2 on
the abundance of species 1 across
all abundances of species 2. For
example, as we just showed, 10
individuals of species 2 reduces
species 1 by 20 individuals, so
species 1 will equilibrate at N1 = 60.
VI. Competition
C. Modeling Competition
1. Intraspecific competition
2. Interspecific competition – Lotka-Volterra Models
and when N2 = 20 (exerting
a competitive effect equal to
40 N1 individuals), then N1
will equilibrate at N1 = 40.
VI. Competition
C. Modeling Competition
1. Intraspecific competition
2. Interspecific competition – Lotka-Volterra Models
And, when species 2 reaches an
abundance of 40 (N2 = K1/α12) it
drives species 1 from the
environment (competitive exclusion).
In this case, species 1 equilibrates at
N1 = 0.
So, this line describes the density at
which N1 will equilibrate given a
particular number of N2 competitors
in the environment. This is the
isocline describing dN/dt = 0.
VI. Competition
C. Modeling Competition
1. Intraspecific competition
2. Interspecific competition – Lotka-Volterra Models
Generalized isocline for
species 1.
VI. Competition
C. Modeling Competition
1. Intraspecific competition
2. Interspecific competition – Lotka-Volterra Models
And for two competing species, describing their effects on one
another.
VI. Competition
C. Modeling Competition
1. Intraspecific competition
2. Interspecific competition – Lotka-Volterra Models
Now, if we put these isocline together, we can describe the possible
outcomes of pairwise competition.
If the isoclines align like this,
then species 1 always
wins.We hit species 2's
isocline first, and then as
abundances increase, species
2 must decline while species 1
can continue to increase.
Eventually, species 2 will be
driven to extinction and
species 1 will increase to its
carrying capacity.
VI. Competition
C. Modeling Competition
1. Intraspecific competition
2. Interspecific competition – Lotka-Volterra Models
Now, if we put these isocline together, we can describe the possible
outcomes of pairwise competition.
If the isoclines align like this,
then species 2 always wins.
We hit species 1's isocline
first, and then as abundances
increase, species 1 must
decline while species 1 can
continue to increase.
Eventually, species 1 will be
driven to extinction and
species 2 will increase to its
carrying capacity.
VI. Competition
C. Modeling Competition
1. Intraspecific competition
2. Interspecific competition – Lotka-Volterra Models
Now, if we put these isocline together, we can describe the possible
outcomes of pairwise competition.
The effects are more interesting if
the isoclines cross. There is now
a point of intersection, where
BOTH populations have a nonzero equilibrium. This is
competitive coexistence. Here it
is stable - a departure from this
point drives the dynamics back to
this point. Essentially, each
species reaches it's own carrying
capacity before it can reach a
density at which it would exclude
the other species.
VI. Competition
C. Modeling Competition
1. Intraspecific competition
2. Interspecific competition – Lotka-Volterra Models
Now, if we put these isocline together, we can describe the possible
outcomes of pairwise competition.
Here the isocline cross, too. But
each species reaches a density at
which it would exclude the other
species before it reaches its own
carrying capacity. So, although an
equilibrium is possible
(intersection), it is unstable... any
deviation will result in the
eventual exclusion of one species
or the other.
VI. Competition
C. Modeling Competition
1. Intraspecific Competition
2. Interspecific Competition – Lotka-Volterra Models
- need to do a competition experiment first, to measure α’s, to predict
outcomes of other competition experiments
- don’t know anything about the nature of the competitive interaction… what
are they competing for?
VI. Competition
C. Modeling Competition
1. Intraspecific Competition
):
2. Interspecific
Competition – Lotka-Volterra Models
3. Tilman’s Resource Models (1982)
3.Tilman's Resource Models (1982)
):
Isoclines graph population
growth relative to resource ratios
(2 resources, R1, R2)
CA = Consumption rate of sp. A.
So, species A consumes 3
units of resource 2 for every
unit of resource 1.
3.Tilman's Resource Models (1982)
):
Isoclines graph population
growth relative to resource ratios
(2 resources, R1, R2)
CA = Consumption rate of sp. A.
So, species A consumes 3
units of resource 2 for every
unit of resource 1.
BUT: It needs more resource 2;
it can by on a small amount of
resource 1.
3. Tilman's Resource Models (1982)
Isoclines graph population
growth relative to resource ratios
): R1, R2)
(2 resources,
CA = Consumption rate of Sp. A.
Resource limitation can occur in
different environments with
different initial resource
concentrations (S1, S2).
So, in S2, the population
becomes limited by the lower
supply of R2. The lower supply
of R1 in S1 is not a problem
because the species uses this
resource so slowly.
Species B requires more of both
resources than species A.
Species B requires more of both
resources than species A. So, no
matter the environment and no
matter the consumptions curves
(lines from S), the isocline for
species B will be "hit" first. So,
Species B will stop growing, but
Species A can continue to grow and
use up resources.... this drops
resources below B's isocline, and B
will decline.
Species B requires more of both
resources than species A. So, no
matter the environment and no
matter the consumptions curves
(lines from S), the isocline for
species B will be "hit" first. So,
Species B will stop growing, but
Species A can continue to grow and
use up resources.... this drops
resources below B's isocline, and B
will decline. So, if one isocline is
completely within the other, then
one species will always win.
If the isoclines intersect, coexistence
is possible (there are densities where
both species are equilibrating at
values > 1).
If the isoclines intersect, coexistence
is possible (there are densities where
both species are equilibrating at
values > 1). Whether this is a stable
coexistence or not depends on the
consumption curves. Consider
Species B. It requires more of
resource 1, but less of resource 2,
than species A. Yet, it also consumes
more of resource 1 than resource 2 - it
is a "steep" consumption curve. So,
species B will limit its own growth
more than it will limit species A.
If the isoclines intersect, coexistence
is possible (there are densities where
both species are equilibrating at
values > 1). Whether this is a stable
coexistence or not depends on the
consumption curves. Consider
Species B. It requires more of
resource 1, but less of resource 2,
than species A. Yet, it also consumes
more of resource 1 than resource 2 - it
is a "steep" consumption curve. So,
species B will limit its own growth
more than it will limit species A. This
will be a stable coexistence for
environments with initial conditions
between the consumption curves (S3).
If the consumption curves were
reversed, there would be an unstable
coexistence in this region.
3. Tilman's Resource Models (1982)
- Benefits:
1. The competition for resources is defined
3. Tilman's Resource Models (1982)
- Benefits:
1. The competition for resources is defined
2. The model has been tested in plants and plankton and confirmed
3. Tilman's Resource Models (1982)
- Benefits:
1. The competition for resources is defined
2. The model has been tested in plankton and confirmed
Cyclotella wins
Cyclotella
Stable Coexistence
PO4 (uM)
Asterionella wins
Asterionella
SiO2 (uM)
3. Tilman's Resource Models (1982)
- Benefits:
1. The competition for resources is defined
2. The model has been tested in plants and plankton and confirmed
3. Also explains an unusual pattern called the "paradox of enrichment"
3. Tilman's Resource Models (1982)
- Benefits:
1. The competition for resources is defined
2. The model has been tested in plants and plankton and confirmed
3. Also explains an unusual pattern called the "paradox of enrichment"
If you add nutrients, sometimes the diversity in a system drops... and one
species comes to dominate. (Fertilize your lawn so that grasses will dominate...
huh?)
If you add nutrients, sometimes the diversity in a system drops... and one
species comes to dominate. Change from an initial stable coexistence scenario (S1)
to a scenario where species A dominates (S2).